Separator for electric storage batteries



Nov. 28, 1950 E.A R. DILLEHAY ETAL 2,531,504

-A SEPRATOR FOR ELECTRIC STRAGE BATTERIES l Filed June 12, 1944 am@ RWM K ,87M (as VENTOR Patented Nov. 28, 1950 SEPARATOR FOR ELECTRIC STORAGE BATTERIES Edward R. Dillehay, Glen Ellyn, and Robert D.

Schuetz, Chicago, Ill., assignors to The Richardson Company, Lockland, Ohio, a corporation of Ohio Application June 12, 1944, Serial No. 539,864

Our invention has to do with separators for use between the plates of electric accumulators, such as are employed in automobiles, by way of example. The main object of the invention is the solution of the fundamental problems inyherent in the formation of inexpensive and satisfactory separators from sheets of felted fibers.

Hitherto, efforts to produce separatorsv from.

such sheetspaper webs being exemplary-have encountered serious diiiculties. separators must be strong, even in the presence of electrolyte. They must be porous to permit the passage of electrolyte, and to permit electrolytic interchange between the plates. 'I'hey must be resistant to acid and electrolytic action. They must not disintegrate or produce deleterious substances or slimes. They must be insulating per se along with the other necessary qualities. The attainment of all of these characteristics has been found so diilicult that the art has turned eitherto naturally occurring substances, like wood, which are not fully satisfactory, or to fabricated panels of acid resistant material in which porosity is attained by expensive techniques. Y

Ancillary objects of our invention include modes of obtaining the necessary characteristics and combinations of qualities in fibrous; felted materials.

'Ihese and other objects of our invention, which will be set forth hereinafter or Willbe apparent to one skilled in the art upon reading these specifications, we accomplish by that` procedure,

1 Claim. (Cl. 13B-145) produced from in that 4certain combination and arrangementofT n elements, and in that article of which we will now describe some exemplary embodiments. Reference is made to the drawings wherein:k

Figure l is a perspective view ,of al separator made in accordance with our invention.

Figure 2 is a sectional view of a modified separator.

rator showing another form of :pro

permitting circulation of electrolyte.

resistance and resistance to electrolytlc action in felted sheets consisting of or `comprising nonacid resistant bers, without destroying the porosity of the sheets, by treating the ufibers .in the sheet with furfuryl alcohol polymers or resins under conditions hereinafter outlined. Of importance in this connection are the characteristics of the sheet and its fibers, the impregnating materials and solutions, the amount of catalyst, the presence of a wetting agent, the total quantities of resinous substances employed, in relation to Vthe kind and qualities of the bers, and other factors which 'we shall describe.

1. The felted web The felted material employed should be, for the average separator, between 20 and 40 mils in thickness. It should have an absorbent or open structure; but too great absorptivity is detrimental. If the sheet is too hard and non-absorptive, its resistance to electrolytic interchange will be too high. If it is too absorptive, it may pick up too much of the resinous lmpregnant, and suffer from the same defect, due to plugging.

The paper or felted sheet may be formed from substantially any type of celluloslc ber, but we prefer to use a felted structure which has fairly long and strong lbers. Cellulosic fibers differ somewhat as to their inherent acid resistance, and fibers which are superior in this quality may be used. We have not, however, found any cellulosic fiber which has sufficient inherent resistance not to require the resin treatment hereinafter described.

An excellent paper for our purpose is a 30 mil I pare of the krafelt type. This may be made either from a sulphate or from a sulphite pulp base; but the bers in the pulp have been given a treatment in caustic to make them curly and soft. Thus, an absorbent impregnating sheet is x fibers otherwise not as satisfactory. Any type of paper of satisfactory absorptivity and strength may, however, be used. vA good, ragbase paper is quite serviceable. Excellent results are obtained with any plain, pure cellulose paper. In some cases, in order to secure yadded strength y .Y 4o Figure 3 is a partial perspectivejview of va sepatuberance .for

after long exposure to acid, we may add a moder- Vate amount ofva longer, stronger or more acidproof type of fiber to the felted structure. As

illustrative of :such reinforcement, we may add 10 or 15% of acid-washed Blue African Asbestos,

y or l0. or 15% of fine filament glass ber. Again,

animal hair vhaving good acidresistance, sisal fiber, strong rope fiber, -lignin-enriched Wood fiber, or fibery from redwood bark, may be used for reinforcement. Some of these fibers may be r used alone.` For'example, in our'process we have made very @satisfactory .separators with paper felted from redwood bark fiber alone, this ber having rgoodlstrength characteristics after long exposure to-acid. v

Yet again, composite webs may be employed. Anvexemplary structure is a center web (woven or felted) of glass fiber with celluloslc nber deposited on it on either side. Again, a main webv of cellulosic fiber may have deposited on it upon one side a thin, layer of glass fiber, the glass side being placed in the battery next the positive plates to cut down burning or charring of the separator.

2. Preparation of the 'resin The preparation of the resin impregnant is important, for reasons which will presently be apparent. The resin should unitewith and acid proof the fibers, while leaving the sheet satisfactorily porous. While it is possible Aby carefully controlled and repeated treatments to impregnate a web with furfuryl alcohol and produce all polymerization in situ, we do not prefer to do this,.

but instead, prefer to produce a controlled prepolymerization whereby to bring the resin to a` I -proper end point, the resinous layer (when cooled to room temperature) is a mobile liquid of relatively low viscosity. It is important that the polymerization be not carried too far and that a high molecular weight resin be not produced at this stage.

The acid acts as a catalyst in the polymerization. Other catalysts may be emloyed, including other acids, substances having a suiiiciently acid reaction, and other substances such as boron tri-fluoride.

The water is decanted from the resin; and to the resin at this point we add a small amount of a wetting agent, such as Aerosol" (dioctylsulpho-sodium succinate). Other wetting agents. soluble in the resin or the resin solution next described may be employed. We ordinarily use about 3% of wetting agent, based on the amount of alcohol or other solvent.

The resin, formed as above, is dissolved in 100 cc. of 95% ethyl alcohol. The impregnating varnish in this condition is stable and can be stored for some time without increasing in molecular weight or becoming too thick.

Just prior to treating the paper web'with the resinous varnish, we add to each 100 cc. of the varnish 1/2 cc. of l-normal sulphuric, acid, or equivalent amounts of other catalysts if used. When this is done, the varnish must be used within a few hours, or the resin will be found to have advanced to a non-penetrating stage. A

The amount of resin carried into the web is important, and should be between substantially 25% and substantially 70% of the combined weight of liber and resin solids. Best results are usually obtained with about 45% resin and paper `by weight. The quantity of resin may advantageously be modified with respect to the kind and character of the fibers and of the web, in view of ascertained end results. In the impregnating step, the ultimate resin content is regulated by the absorbency of the paper, the resin content of the varnish, the amount of acid catalyst'used, the temperature of the heating chamber, and the mechanical `arrangement of the squeeze rolls, scraper bars and the like used for removing excess varnish during treatment, as will be readily understood by the skilled worker.

In the drying chamber the solvent is removed, and further polymerization takes place. It should not be assumed that the ultimate in polymerization takes place in this chamber, or that it is necessarily desirable to have it do so. The product from the drying chamber should be dry to the feel and strong enough to handle and to form into finished separators; but ultimate and final polymerization preferably occurs in the storage battery in the presence of the acid electrolyte.

The use of a wetting agent is necessary in the manufacture of a successful separator in accordance with our process. The wetting agent not only brings the resin into better union' with the bers, more perfectly acid-proofing them, but it appears to have another effect also. When a wetting agent is not used, unless the separators are put into service within a few hours after impregnation, they are found to be of very high resistance and substantially impermeable to the electrolyte. We do not wish to be bound by theory, but we believe that the impregnated and dried separators are initially imperfectly porous, and are characterized by or tend to form internal films of resin. Battery acid, striking the resin, rapidly completes the polymerization, which may occur before the acid has penetrated the films. Thus, the acid proof internal barriers are made permanent. But when a wetting agent is incorporated in the resin, the acid appears to strike through the separator before polymerization is completed; the separator is not only rendered porous, but the .resin is polymerized to completion when in a porous condition. The

, wetting lagent itself is probably destroyed by the catalyst is desired to accelerate the polymerizal paper, making them considerably weaker.

3. Impregnating and treating the web The paper ,or reinforced web may be treated with the varnish in any suitable machine having impregnating means and a drying chamber for removing the solvent and advancing the resin. The well-known Waldron4 saturating machine is suitable. A saturating tower may .also be used.

\ saturated, as we have described, ribs or the like battery acid after a short exposure.

In this way we have succeeded in producing from felted webs separator bodies having all of the necessary qualities for service.

4. Circulation means and their application JAfter the paperhas been acid proofed and maybe applied to one surface of it to permit 4circulation of the electrolyte in the battery. We

have employed for this purpose soft rubber strips (2 in Figure l), aiiixed by means of an acidproof adhesive to the surface'of the separator body I. A soft rubber compound, usually of reclaimed rubber, is formed into a continuous sheet of the proper thickness which, after curing, is slit into narrow strips of the desired width for the ribs. 'I'he ribs can be applied in a continuous operation to a continuous separator body.

Other substances will serve for the ribs. We may, for example, employ a paper stock of proper thickness impregnated with our resin, cut into s rib width and adhesively applied. Also, we may fold our separator body material or emboss it, as indicated at 3 in Figure 2, to form protuberances, while the separator body is still in the ilexible and pliable stage during the drying process.

The ribs need not be continuous ribs extending'across one dimension of the separator. Small circular or other pieces of acid proof substance may be employed. Yet again, we have made satisfactory .ribs or protuberances by mixing a quick-setting, acid-catalyzed,- phenolic resin with nous body associated therewith as anl impregnant and having sufficient continuity to be selfsustalning, in which the porosity is due in preponderant degree to the wicking action of the said cellulosic ilbers, said separator in use being subject to further polymerization of the resin by reason of the catalytic action of the battery acid and an increase in porosity due to at least paran acid-proof mineral filler to provide a thick,

heavy liquid or pasty substance. This is applied to the separator bodyby suitable means in the form of interspaced dots 4 or in the form of lnterspaced stripes (5 in Figure 3) of proper thickness. The resin-1111er mixture may be allowed to set up at room temperature or the polymerimtion can be accelerated by heat. `Protuberances or ribs formed in this fashion are very satisfactory, inexpensive, and exhibit good adhesion to the separator body.

Modiilcations may be made in our invention without departing from the spirit of it. Having thus described our inventionv in exemplary embodiments, what we claim as novel and desire to secure by Letters Patent is:

A storage battery separator consisting of an absorptive felted iibrous sheet containing at least 85% of cellulosic bers, said sheet being saturated with partially polymerized furfuryl' alcohol containing a wetting agent, said sheet containing resin solids therein in the amount of between substantially 25% and substantially 70% of the combined weight of the ilbrous sheet and resin, the saturated sheet having suillcient strength for handling in the building of a storage battery, and and having a skeleton of ielted fibers and a resitial destruction of the cellulosic fibers through the action of battery acid thereon, the penetration of said separator by the battery acid being facilitated by said wetting agent.

EDWARD R. DI'LLEHAY. ROBERT D. SCHUETZ.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,206,983 Bliss Dec. 5, 1916 1,297,644 Boyer Mar. 18, 1919 1,357,378 Boyer Nov. 2, 1920 2,028,091 Jaeger June 14, 1936 2,108,748 Harner et al Feb. 15, 1938 2,117,382 Wells May 17, 1938 2,345,966 Friedler Apr. 4, 1944 2,397,453 White May 26, 1946 FOREIGN PATENTS v Number .Country Date 347,012 Great Britain Apr. 23, 1931 OTHER REFERENCES Ellis, "The Chemistry of Synthetic Resins, Page 522 (1935). 

